CA1241426A - Device for controlling at least one vhv or uhv circuit breaker from a fault signal - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A device for controlling at least one very-high-voltage or ultra-high-voltage circuit breaker in response to a fault signal, which control device comprises a circuit for detecting the fault signal and for time-delaying the same to produce a trip signal. A low power electromechanical relay is energized in response to the trip signal to close its contacts very rapidly and without rebound. Each circuit breaker is associated with an electronic power amplifier responsive to the closure of the contacts of the low power relay to supply the corresponding circuit breaker with a current which causes opening of the latter. Each circuit breaker is therefore opened very rapidly upon occurrence of the trip signal due to the electronic structure of each power amplifier and the very fast , without rebound operation of the low power electromechanical relay.

Description

The present invention relates to a device for controlling at least one very-high-voltage l~HV) or ultra-high-voltage (U~IV) circuit breaker in response to a signal indicating a fault within an electric system protected thro~gh this circuit breaker.
It should be pointed out here that, for the purpose of the present disclosure, the terms avery-high-voltage (VHV) and ~<ultra-high-voltage ~UHV) >~ are intended to designate any voltage equal to or higher than 25 kV.
Conventionally, the control devices of the above-defined type comprise a circuit for detecting the fault signal, usually in the form of a pulse signal supplied by a protection relay, while rejecting disturbances signals which can be possibly applied as input to the detecting circuit.
A delay circuit is also provided for appropriately time-delaying the leading edge and the trailing edge of the fault signal to thereby produce a trip signal. The leading edge of the fault signal is delayed by a time period ~for e~ample 3ms) to prevent opening of said at least one circuit breaker in response to noise voltage peaks of short duration inherent to VHV or UHV electric systems. This delay of 3 ms ensure that such noise voltage peaks will not cause opening of said at least one circuit breaker. On the other hand, the trailing edge of the fault signal is delayed by a time period (for example 30 ms) so that the trip signal remains during this period of time after disappearance of the fault signal due to opening of the circuit breaker, to ensure completion of the opening operation of the circuit breaker.
In the presently known devices for controlling VHV
or UHV circuit ~reakers, an electromechanical relay is associated with each circuit breaker to supply it with a current in response to the trip signal, thereby causing opening the circuit breaker. As the current necessary to cause opening of a VHV or UHV circuit breaker is of the order of 12 amperes, the electromechanical relays must be provided with big contacts which can support such a relatively high magnitude of current. It is also well known that a VHV or UHV circuit breaker must be opened very rapidly upon occur-rence of an electrical fault indicated by the fault signal.
Unfortunately, the time taken by an electromechanical relay to close its contacts increases with the current these con-tacts can support. Indeed, the inertia of the armature supporting the big contacts of a high power relay is higher than the inertia of the armature of a low power relay.
Another factor which increases the closure time is the dis-tance between the contacts when open to provide a suitableinsulation therebetween taking into consideration the voltage applied between these open contacts. Moreover, such electro-mechanical relays produce rebounds of the contacts on each other upon closure of the same, thereby retarding opening of the circuit breakers.
Of course, it is possible to increase the speed of closure of the contacts of such electromechanical relays.
However, this cannot be carried out without also increasing the time of rebound of the contacts upon closure of the latter.
Consequently, the electromechanical relays used in the conventional circuit breaker control devices are not suitable to meet with the speed requirements in the control of VHV or UHV circuit breakers.
Presently, the reduction of the time taken to open a VHV or UHV circuit breaker is directed towards the design o~ the circuit breakers themselves and the detection of the fault, for example, through protection relays.
An object of the present invention is therefore to replace the electromechanical relays used in the conven-tional circuit breaker control devices by a circuit designed to respond very rapidly to a trip signal to cause opening of at least one VHV or UHV circuit breaker, thereby eliminating the drawbacks of such electromechanical relays.
More particularly, according to the present inven-tion, there is provided a device for controlling a very-high-voltage or ultra-high-voltage circuit breaker in response to a signal indicating an electrical fault within an electric system protected through the circuit breaker, comprising:

means for detecting the fault signal and for delivering a trip signal in response thereto;
low power switching means responding very rapidly to the trip signal to produce a command signal; and an electronic power amplifier for supplying a current to said circuit breaker in response to said command signal, which current commands opening of the circuit breaker;
whereby opening of the very-high-voltage or ultra-high-voltage circuit breaker is commanded very rapidly upon occurrence of the trip signal due to the electronic struc-ture of the power amplifier and to the very fast response of the low power switching means to the trip signal.
Consequently, the control device according to the present invention eliminates the above discussed drawbacks of the conventionally used electromechanical relays by replac-ing such relays by low power switching means associated with an electronic power amplifier for supplying very rapidly to the circuit breaker the current which causes opening of the latter.
Of course, the circuit breaker control device may be designed for simultaneously controlling a plurality of VHV or UHV circuit breakers.
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description of a preferred embodiment thereof, made with reference to the accompanying drawings in which:
Figure 1 is a functional block diagram of a device according to the present invention for controlling four VHV
or UHV circuit breakers, and Figure 2 illustrates details of the circuit of the control device of Figure 1.
Referring now to Figure 1 of the drawings, the control device CD according to the present invention receives on its input IN a fault signal delivered from a protection relay PR. Such a protection relay is responsive for example to the current through a VHV or UHV electric energy trans-mission line or any other VHV or UHV electric network or 5ystem protected through four circuit breakers CBl t~ CB4, all controlled through the device CD. When an electrical fault appears on the line, network or system, for example a ground fault current, the protection relay PR produces a fault signal under the form of a pulse by delivering a certain direct current ~DC) voltage level on the input IN.
No signal is otherwise applied on this input IN by the pro-tection relay PR. This type of protection relay is well-known in the art and for that reason it will not be further elaborated.
The control device CD comprises an input circuit

2 for receiving as input any fault signal produced through the protection relay PR. This circuit 2 comprises an input filter allowing transmission of a fault signal while stopping disturbance signals, and a circuit to block any signal having an amplitude lower than a predetermined value.
A delay circuit 3 supplied from a power supply circuit 1 time-delays the leading and trailing edges of the fault signal transmitted through the input circuit 2 to this delay circuit 3 so as to produce a trip signal applied to a low power switching circuit 4.
In response to the trip signal from the delay circuit 3, the low power switching circuit 4 activates a current amplifier stage 5, which amplifier stage 5, when activated, supplies the four VHV or UHV circuit breakers CBl to CB4 with a current causing opening of these four circuit breakers.
The control device CD according to the present invention will now be described in details with reference to Figure 2 of the drawings.
The power supply circuit 1 comprises two input terminals 10 and 11. A DC voltage V is applied between these two input terminals 10 and 11 of the circuit 1, the terminal 11 corresponding to the ground of the circuit of the control device CD. The voltage V may be delivered for example by an available auxiliary DC supply. It can of course also be supplied from an additional DC source especially provided for this purpose.
The supply circuit 1 also comprises a varistor 12 connected between the terminals 10 and 11. The function of the varistor 12 is to protect the control device ~D against possible transitory overvoltages applied to the input terminals 10 and 11 of the supply circuit 1.
A resistor 13 cooperates with a Zener diode 1~ to supply to the delay circuit 3 a suitable DC voltage Vz produced across the Zener diode 14. The resistor 13 also forms with a capacitor 15 a low-pass filter which eliminates any high-frequency disturbances in the DC voltage V .
The input circuit 2 is designed so that only a fault signal delivered from the protection relay PR and applied on an input terminal 20 of the circuit 2 will cause opening of the four breakers CBl to CB4 by the control device of the invention.
For this purpose, the input circuit 2 comprises a resistor 21, a resistor 22, and a capacitor 23 constituting a rapid discharge filter for blocking a voltage on the input 20 which could be generated upon connection of a very long cable to the input terminal 20.
The resistor 24 and the capacitor 25 form a low-pass filter provided to obtain a better elimination of the high frequency disturbances applied on the input 20.
The addition of the avalanche-breakdown reverse voltages of two Zener diodes 26 and 27 determines a threshold voltage under which a signal on the input terminal 20 is not transmitted to the delay circuit 3 and consequently does not cause opening of the four breakers CBl to CB4. By appropria-tely selecting the diodes 26 and 27, this threshold voltage can be adjust~d at any suitable or required level. Another function of the Zener diode 27 is to reduce the voltage value of a fault signal applied on the input terminal 20 to a level acceptable by the delay circuit 3.

The function of the delay circuit 3 is to time-delay the leading edge as well as t~e trailing edge of a fault signal applied on the input terminal 20.
The delay circuit 3 includes for this purpose two resistors 31 and 32 and a capacitor 33. A diode 30 determines the charge and discharge paths of the capacitor 33. More specifically, the capacitor 33 is charged b~ a fault signal appearing at the output 28 of the input circuit 2 through the diode 30 and the resistor 32, while this capacitor 33 is discharged through the resistors 31 and 32 when the signal at the output 28 disappears. The charge time is therefore determined by the values of the capacitor 33 and the resistor 32, and the discharge time by the values of the capacitor 33 and the resistors 31 and 32. By appro-priately selecting the values of the resistors 31 and 32 and of the capacitor 33, it is consequently possible to obtain the required time constants for the charge and discharge of the capacitor 33. It is evident here that the charge time constant is shorter than the discharge time constant.
A comparator 37 is-supplied with the voltage Vz across the Zener diode 14 of the circuit 1 through its supply inputs 38 and 39, and compares the voltage across the capa-citor 33 with a reference voltage produced at the intersection point 36 of two series-connected resistors 34 and 35 forming a voltage divider supplied with the voltage Vz across the diode 14. As illustrated on Figure 2, the voltage across the capacitor 33 is supplied to the positive signal input ~+) of the comparator 37, while the re~erence voltage at point 36 is supplied to the negative signal input (-) of the comparator 37.
The comparator 37 produces on its output a trip signal having a high logic level as long as the voltage across the capacitor 33 is equal to or higher than the reference voltage at point 36. On the contrary, the compa-rator 37 produces on its output a signal having a low logic level as long as the voltage across the capacitor 33 is lower than the reference voltage at point 36.
~5 the capacitor 33 is charged upon occurrence of the leading edge of a fault signal on the input terminal 20 and discharged upon occurrence of the trailing edge of the same fault signal, the comparator 37 delays appropriately the leading and trailing edges of the fault signal by comparing the voltage across the capacitor 33 with the reference voltage at point 36. As explained hereinabove, the time of delaying of the leading edge is determined by the values of the resistor 32 and of the capacitor 33 while the time of delaying of the trailing edge is dstermined by the values of the resistors 31 and 32, and by the value of the capacitor 33. As also stated above, the leading edge of the fault signal may be delayed by a time period of about 3 ms to prevent opening of the circuit breakers in response to noise voltage peaks of short duration inherent to VHV or UHV
electric systems, while the trailing edge of the fault signal may be delayed by a time period of about 30 ms so that the trip signal from the comparator 37 remains during this period of time after disappearance of the fault signal due to opening of the four circuit breakers to ensure completion of the opening operation of these circuit breakers CBl to CB4.
The control device CD further comprises a low power switching circuit 4 as well as a current amplifier stage 5.
The switching circuit 4 and the amplifier stage 5 are speci-fically designed to replace the electromechanical relays conventionally used to control VHV or UHV breakers as dis-cussed in the preamble of the present disclosure. They have a very fast response and operate without rebounds whereby the drawbacks of the conventional relays are eliminated.
The signal at the output of the comparator 37 is transmitted to the base of a switching transistor 42 through the input 40 of the switching circuit 4 and a resistor 41.
When the voltage across the capacitor 33 becomes equal to the reference voltage at point 36 during charging of this capacitor 33 by a fauIt signal, the output of the comparator 37 takes a high logic level ~trip signal), whereby a base current is supplied to the transistor 42 to enable the same to drive a current flowing through a coil 44 of a low-power electromechanical relay 43. This current flows through a terminal 48 to which is applied the DC
voltage V , also supplied to the power supply circuit 1, through a resistor 46, through the coil 44 and through the collector-emitter junction o~ the conducting transistor 42, which has its emitter grounded. The relay 43 is provided with four pairs of contacts such as 45 which are closed as long as the coil 44 is energi~ed, i.e. as long as the trip signal is present on the input 40.
When the voltage across the capacitor 33 becomes lower than the reference voltage at point 36 during discharge of this capacitor 33, the output of the comparator 37 takes a low logic level thereby turning the transistor 42 off by depriving it from its base current. The coil 44 is then de-energized to open the four pairs of contacts 45. These four pairs of contacts remain open until a new trip signal appears on the input 40.
A diode 47 is connected in parallel to the coil 44 as shown on Figure 2 to inhibit any overvoltage across the coil 44 caused by a sudden decrease of current there-through upon turning off of the transistor 42.
The relay 43 may advantageously be a mercury REEDrelay~ Such a mercury relay has a very fast response and a good insulation between its coil and its contacts, and operates without causing rebounds of its contacts on each other upon closing of the same. Conventional REED relays or opto-coupling devices may also alternatively be used.
~ s illustrated on Figure 2 of the attached drawings, the current amplifier stage 5 comprises a current power amplifier for each of the four VHV or UHV breakers CBl to CB4. Each current amplifier comprises a transistor 51 asso-ciated ~ith one of the four pairs of contacts 45 of the relay ~L~? ~

43, and a txansistor 52. The collectors of the transistors 51 and 52 are connected to an input terminal 54 to which is applied the DC voltage V , while the emitter of the transistor 51 is connected to t~e base of the transistor 52.
The emitter of the transistor 52 is connected to an output terminal 55 of the current amplifier, an activation coil 50 of the corresponding breaker (CBl to CB4) being connected between the terminal 55 and the ground as illus-trated for only one of the current amplifiers of the stage5 for the purpose of simplification of the drawings.
Upon closure of the pairs of contacts 45 of the relay 43, the base and the collector of each transistor 51 are interconnected through these pairs of contacts, whereby the transistors 51 and 52 of each current amplifier drive a current to the coil 50 of the corresponding VHV or UHV
breaker to cause opening of the same. The closures of the pairs of contacts 45 of the relay 43 therefore constitute command signals to the four current amplifiers of the stage 5 to cause opening of the four VHV or UHV circuit breakers.
A varistor 53 is connected between the input terminal 54 and the output terminal 55 of each current amplifier of the stage 5 to protect the controlling device against overvoltages generated by the opening of the circuits includin~ the coils 50 of the four circuit breakers CBl to CB4.
The indicia 1 to 4 associated with the reference numerals 51 to 55 on Figure 2 of the drawings identify each of the four current amplifiers ~indicia 1 to 4) associated with the four VHV or UHV brea~ers CBl to CB4, and designate their respective input 54, transistors 51 and 52, varistor 53, and output 55.
It can be easily appreciated from Figure 2 and the above description that due to the very fast response of the switching circuit 4 to the trip signal from the comparator 37 and due to the electronic structur~ of the cuxrent amplifier stage 5, the four circuit breakers CBl to CB4 can be opened very rapidly in response to a trip signal on the input 40.
In the case of VHV or UHV circuit breakers controlled through an alternating current applied to the coil 50, the switching circuit 4 and the amplifier stage 5 may use components such as opto-triacs, triacs, silicon controlled rectifiers (SCR), etc..., with the same results and efficiency~
Moreover, as the circuit breakers CBl to CB~ are controlled through current puIses, the transistors 51 and 52 of each current amplifier of the stage 5 are advantageously selected to support a relatively high current during a limited time period. These current amplifiers may of course take other possible forms.
Although the present invention has been described hereinabove by way of a preferred embodiment thereof, it should be pointed out that this preferred embodiment may be modified at will, within the scope of the appended claims, without altering or changing the nature of the present invention.

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for controlling a very-high-voltage or ultra-high-voltage circuit breaker in response to a signal indicating an electrical fault within an electric system protected through said circuit breaker, comprising:
means for detecting said fault signal and for delivering a trip signal in response thereto;
low power switching means responding very rapidly to said trip signal to produce a command signal; and an electronic power amplifier for supplying a current to said circuit breaker in response to said command signal, which current commands opening of the circuit breaker;
whereby opening of said very-high-voltage or ultra-high-voltage circuit breaker is commanded very rapidly upon occur-rence of said trip signal due to the electronic structure of the power amplifier and to the very fast response of the low power switching means to said trip signal.

2. A control device according to claim 1, wherein said detecting and delivering means comprise input filter means allowing transmission of said fault signal while blocking disturbance signals.

3. A control device according to claim 1, in which said detecting and delivering means comprise Zener diode means for blocking any signal having an amplitude lower than a predetermined amplitude value.

4. A control device according to claim 1, wherein said fault signal is a pulse signal having a leading edge and a trailing edge, and wherein said detecting and deliver-ing means comprise means for time-delaying the leading and trailing edges of said pulse signal in order to produce said trip signal.

5. A control device according to claim 4, in which said time-delaying means comprise means for time-delaying the leading edge of said pulse signal by a first predetermined time period, and means for time-delaying the trailing edge of said pulse signal by a second predetermined time period different from said first predetermined time period.

6. A control device according to claim 5, wherein said means for time-delaying the leading edge of said pulse signal by a first predetermined time period and said means for time-delaying the trailing edge of said pulse signal by a second predetermined time period comprise a resistive and capacitive circuit associated with a comparator circuit, said comparator circuit delivering said trip signal.

7. A control device according to claim 1, wherein said switching means comprise a low power electromechanical relay comprising a pair of contacts associated with the electronic power amplifier, said electromechanical relay being designed to close its pair of contacts without rebound.

8. A control device according to claim 7, in which said electromechanical relay comprises a coil, said low power switching means comprising a transistor responsive to said trip signal to energize the coil of the electro-mechanical relay in order to close said pair of contacts.

9. A control device according to claim 7, in which said electronic power amplifier comprises a first transistor having a collector and a base, said pair of contacts comprising a first contact connected to said collector of the first transistor and a second contact connected to the base of the first transistor, whereby closing of said pair of contacts establishes an inter-connection between the collector and the base of the first transistor to turn the latter on.

10. A control device according to claim 9, in which the electronic power amplifier comprises a second transistor connected to said first transistor so that turning on of the first transistor turns the second transistor on in order to supply through this second transistor said current to the circuit breaker to command opening of the latter.

11. The control device of claim 10, wherein said circuit breaker comprises a trip coil, said current being supplied to said trip coil of the circuit breaker.

12. The control device of claim 1, in which said electronic power amplifier comprises a first transistor for delivering said current to said circuit breaker upon turning on thereof, and a second transistor for turning said first transistor on in response to said command signal.

13. The control device of claim 1, in which said electronic power amplifier is designed to support a high current during a limited time period.

14. The control device of claim 1, wherein said circuit breaker comprises a trip coil, and wherein said electronic power amplifier comprises means to supply said current to said trip coil of the circuit breaker to cause opening of the latter.

15. The control device of claim 1, wherein said electronic power amplifier comprises output means provided with means for protecting said power amplifier against overvoltages.

16. The control device of claim 1, in which said low power switching means comprise means for electrically insulating said electronic power amplifier from the remaining of the circuit of said control device.

17. A device for controlling a plurality of very-high-voltage or ultra-high-voltage circuit breakers in response to a signal indicating an electrical fault within an electric system protected through said circuit breakers, comprising:
means for detecting said fault signal and for delivering a trip signal in response thereto;
low power switching means responding very rapidly to said trip signal to produce a plurality of command signals; and a plurality of electronic power amplifiers each supplying a current to a corresponding one of said circuit breakers in response to a corresponding one of said command signals, which current commands opening of said corresponding circuit breaker;
whereby opening of said very-high-voltage or ultra-high-voltage circuit breakers is commanded very rapidly upon occurrence of said trip signal due to the electronic structure of the power amplifiers and to the very fast response of the low power switching means to said trip signal.